1. Field of the Invention
The present invention relates to a method for synthesizing rare-earth oxo isoproxide (Ln5O(O-i-C3H7)13), which is useful as a raw material of a polymerization catalyst or asymmetric synthesis catalyst.
2. Description of the Related Art
La5O(O-i-C3H7)13 is one species of rare-earth oxo isopropoxide (referred to as Ln5O(O-i-C3H7)13 hereinafter, wherein Ln represents a rare-earth element).
Ln5O(O-i-C3H7)13 is useful as a polymerization-catalyst starting material. For example, V. Simic, N. Spassky, L G. Hubert-Pfalzgraf, “Macromolecules”, 1997, vol. 30, pp. 7338-7340 states that oxo isopropoxide of Y or La can be used for a ring-opening polymerization reaction of a lactide.
Ln5O(O-i-C3H7)13 or rare-earth alkoxides beside it are used also as raw materials of various catalytic asymmetric syntheses or polymerization reactions.
About a synthesizing process of Ln5O(O-i-C3H7)13, for example, O. Poncelet, W. J. Sartain, L G. Hubert-Pfalzgraf, K. Folting, K. G. Caulton, “Inorganic Chemistry”, 1989, vol. 28, pp. 263-267 states that metallic yttrium, and mercuric chloride and mercuric acetate as catalysts are added to a mixed solvent of isopropyl alcohol and toluene, the solution is refluxed to cause reaction, and the resultant is subjected to filtration, recrystallization and drying to synthesize Y5O(O-i-C3H7)13 with a yield of 75%.
However, the above-mentioned document O. Poncelet, W. J. Sartain, L G. Hubert-Pfalzgraf, K. Folting, K. G. Caulton, “Inorganic Chemistry”, 1989, vol. 28, pp. 263-267 does not describe partial hydrolysis by the addition of water.
The present inventors tried to conduct the same synthesizing process. As a result, the substance obtained by filtrating the reaction liquid, distilling off the solvent from the filtrate and then drying the residue contained a large amount of components insoluble in an organic solvent such as THF or toluene in some cases. Thus, the reproducibility of the solubility of the substance in an organic solvent was poor. Thus, it was difficult to use the substance as a raw material of an organic synthesis catalyst.
Moreover, the above-mentioned document V. Simic, N. Spassky, L G. Hubert-Pfalzgraf, “Macromolecules”, 1997, vol. 30, pp. 7338-7340 states that La5O(O-i-C3H7)13 was synthesized according to the document O. Poncelet, W. J. Sartain, L G. Hubert-Pfalzgraf, K. Folting, K. G. Caulton, “Inorganic Chemistry”, 1989, vol. 28, pp. 263-267, but includes no description about the identification of the product.
The present inventors tried the same synthesizing process. As a result, the concentration of isopropyl alcohol in the reaction solution was as low as 50% so that the induction period, which ends at a time when the reaction starts, was 20 hours or longer. Thus, the reaction efficiency was poor. Furthermore, the reaction liquid obtained by causing metallic lanthanum and isopropyl alcohol to react with each other contained a solid component in a large amount of about 50% by mole of metallic lanthanum used in the reaction. As a result, the yield of La5O(O-i-C3H7)13 obtained after the solid component was removed by filtration was from 10 to 40%, so that the productivity was poor.
Furthermore, Tamon Okano et al., “The Journal of the Chemical Society of Japan”, 1993, vol. 5, pp. 487-492 describes a process of adding metallic lanthanum in a powdery form and mercuric chloride to isopropyl alcohol, heating and refluxing the solution, and subjecting the resultant to concentration, extraction with benzene, filtration, distillation, drying and recrystallization so as to synthesize La(O-i-C3H7)3.
However, this synthesizing process is not based on partial hydrolysis, either, and is a process similar to the processes described in the documents V. Simic, N. Spassky, L G. Hubert-Pfalzgraf, “Macromolecules”, 1997, vol. 30, pp. 7338-7340, and O. Poncelet, W. J. Sartain, L G. Hubert-Pfalzgraf, K. Folting, K. G. Caulton, “Inorganic Chemistry”, 1989, vol. 28, pp. 263-267. The synthesis yields are also as low as values of 20 to 30%.
Furthermore, JP-A No. 9-157272 discloses a process of adding, to an alcohol, a rare-earth metal and iodine (and a mercuric chloride) as a catalyst to synthesize a rare-earth metal alkoxide. This synthesizing process is not based on partial hydrolysis, either. Moreover, it is unavoidable that the product is contaminated by iodine.
Additionally, G. Westin, M. Kritikos, M. Wijk, “Journal of Solid State Chemistry”, 1998, vol. 141, pp. 168-176 describes a process of synthesizing potassium isopropoxide in a mixed solvent of isopropyl alcohol and toluene, adding water to this solution, and then adding anhydrous ErCl3 to the resultant, thereby causing the reactive components to react with each other, thereby synthesizing Er5O(O-i-C3H7)13.
However, this process has a problem that the anhydrous rare-earth chloride as the raw material is expensive so that production costs increase.
The document G. Westin, M. Kritikos, M. Wijk, “Journal of Solid State Chemistry”, 1998, vol. 141, pp. 168-176 also states that Er5O(O-i-C3H7)13 can be synthesized by causing reaction with metallic erbium in a mixed solvent of isopropyl alcohol and toluene, removing the resultant solid component, which has olive color, distilling the supernatant, drying the residue to yield a pink viscous material with a yield of 40 to 45%, and then hydrolyzing this material partially in a mixed solvent of isopropyl alcohol and toluene.
However, in this process, at the time of removing the solid component from the reaction liquid obtained by the reaction between metallic erbium and isopropyl alcohol, the rare-earth element contained in this solid component is also removed so that a poor yield is given. This process is not according to partial hydrolysis of the olive solid component, either. Additionally, the document never refers to La5O(O-i-C3H7)13.
In short, it has not been known in the prior art that La5O(O-i-C3H7)13 can be yielded by subjecting a solid component obtained by reaction with metallic lanthanum and isopropyl alcohol to partial hydrolysis.
According to reaction between a rare-earth metal and isopropyl alcohol, an unreacted fraction of the rare-earth metal remains as it is in a small amount. In any conventional process, the unreacted rare-earth metal is removed by filtration or decantation. However, the metal is very fine and highly active; thus, when the metal contacts the atmosphere, the metal reacts with oxygen so that the metal ignites immediately. For this reason, in steps in the process, very careful attention is required to be paid.
Furthermore, in the prior art, an unreacted fraction of rare-earth metal has never been inactivated at the same time of synthesizing Ln5O(O-i-C3H7)13.